In-flight refueling (or air-to-air refueling) is an important method for extending the range of aircraft traveling long distances over areas having no feasible landing or refueling points. Although in-flight refueling is a relatively common operation, especially for military aircraft, the aircraft to be refueled (e.g., the receiver aircraft) must be precisely positioned relative to the tanker aircraft in order to provide safe engagement while the fuel is dispensed to the receiver aircraft. The requirement for precise relative spatial positioning of the two rapidly moving aircraft makes in-flight refueling a challenging operation.
There are currently two primary systems for in-flight refueling. One is a hose and drogue system in which a refueling hose having a drogue disposed at one end is trailed behind the tanker aircraft and is engaged by the receiver aircraft. Another system is a boom refueling system. The boom refueling system typically includes a rigid boom extending from the tanker aircraft, with a probe and nozzle at its distal end. The boom also includes boom aerodynamic control surfaces or airfoils (e.g., ruddevators, horizontal and vertical surfaces, and/or flow control surfaces) controlled by a boom operator stationed on the tanker aircraft. The boom aerodynamic control surfaces allow the operator to maneuver the boom with respect to the receiver aircraft. Accordingly, the receiver aircraft is first maneuvered into an in-flight refueling position below and aft of the tanker aircraft. The boom operator then controls the boom aerodynamic control surfaces to position the boom and mate the refueling nozzle with a refueling connection on the receiver aircraft.
In order to accommodate the inevitable relative motion between the tanker aircraft and the receiver aircraft, the refueling boom must be movable, both vertically and laterally. One drawback with using the boom aerodynamic control surfaces to control movement of the boom is that the effectiveness of the aerodynamic control surfaces can be reduced significantly during certain operating conditions (e.g., large lateral deflections and at high Mach numbers). Accordingly, the size of the refueling envelope can be limited. Another drawback associated with boom aerodynamic control surfaces is that such structures require extensive wind tunnel testing and control system development to ensure that the control surfaces provide adequate control of the refueling boom at a variety of operating conditions. Still another drawback with boom aerodynamic control surfaces is that such structures can potentially contact the receiver aircraft during refueling and cause significant damage to the receiver aircraft, the tanker aircraft, and/or the refueling boom itself.